A material for measuring pressure is used in applications to a step of laminating liquid crystal glass, solder printing onto a print substrate, and regulation of pressure between rollers.
As the material for measuring pressure, for example, there is a pressure measuring film represented by Prescale (trade name) provided by Fujifilm Corporation. The pressure measuring film has such characteristic that the film can be used after being cut into an arbitrary size in accordance with a measuring site. Further, the pressure measuring film has such characteristic as capable of measuring surface pressure, differing from a so-called pressure-sensitive copying paper in which a color forming reaction occurs by high line pressure caused by writing pressure.
As an example of the pressure measuring film, a pressure measuring sheet utilizing a color forming reaction between an colorless electron-donating dye precursor and an electron-accepting compound is disclosed (see, for example, Japanese Patent Application Publication (JP-B) No. 57-24852), which is announced to be usable in the measurement of pressure ranging around from 0.1 Mpa to 20 Mpa. For the substrate of the pressure measuring film, generally, a film made of plastic such as polyethylene terephthalate is used.
Recently, as the result of high functionality and high fineness of products, the necessity of measuring the distribution of minute pressures is increasing. For example, for bonding panels using a pressurizing system such as a liquid crystal display and a plasma display, it is frequently carried out within a pressure region of 3 MPa or less for a large area, and the measurement of pressure distribution of 3 MPa or less has become important.
On the other hand, there is disclosed a pressure-sensitive copying sheet that uses substituted metal salt of salicylic acid as a color developing agent and encapsulates dye in a capsule having a polyurea resin/polyurethane resin wall membrane (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 7-96662). Further, a pressure-sensitive recording paper using an amide-based compound is conventionally known (see, for example, JP-A No. 2786510, JP-A No. 3019163, and JP-A No. 3074891), and there are proposed ones using acrylamide copolymer, sulfonamide or a (meth)acrylic acid ester compound as the amide-based compound.